Official Description:
CASTIEL RETURNS — Sam (Jared Padalecki) and Dean (Jensen Ackles) call Castiel (Misha Collins) for help when they investigate a case about several dead police officers who seem to have been killed by the plagues of Egypt. Castiel confirms the staff of Moses was used to kill the cops and tells Sam and Dean that Heaven is in a state of chaos and God’s weapons have been stolen. The three head off to find the thief and come face to face with an old enemy.Bob Singer directed the episode written by Ben Edlund.

[Supernatural] is adding a new angel who’s gone a bit rogue (Balthazar). The possibly recurring character is described as an attractive charmer who appears slightly manic on the surface but carries a great sadness.Source: TV Guide

Balthazar and Castiel have a history: “Remember when Cass (played by Misha Collins) was dragged back to Heaven as a prisoner? Balthazar was actually the only friend who stood up for him,” ‘Supernatural’ executive producer Sera Gamble notes. “During the Apocalypse, Balthazar went AWOL, and Cass thought he was dead. Turns out… not so much.” He will be played by Sebastian Roché.Source: Fancast